It is an effective approach to obtain high-power laser output by spectral beam combining (SBC) technologies. In this paper, a simple SBC system based on the superimposed reflective volume Bragg grating (RVBG) is proposed to reduce the scale of the SBC system. Considering the cross-coupling between the two gratings in a volume, two structure models of the superimposed RVBG-the superimposed RVBG with the same period and the superimposed RVBG with a different period-are analyzed and compared by using the rigorous coupled wave analysis, and their applications for SBC system are discussed. Numerical results show that the superimposed RVBG is easy to be fabricated and has the potential to combine multiple lasers with one volume. Cross-coupling can be neglected for the same period structure when the slant angle divergence is larger than 0.01 rad and for the different period structure when the spectral separation is larger than 1.0 nm. The superimposed RVBG with a different period can achieve high diffraction efficiency simultaneously for each grating with a small slant angle divergence, and is convenient to combine multiple beams with small spectral separation. The effect of wavelength shift on diffraction efficiency can be ignored.
A simple setup for radially polarized beam generation based on the reflecting volume phase grating is proposed to enhance the converting efficiency. The radially polarized beam is obtained by coherently combining the two orthogonally polarized Hermite-Gaussian HG01 and HG10 beams. By using the plane wave decomposition and the three-dimensional rigorous coupled wave analysis approaches, the intensity distribution of the diffracted beam is compared with the respective incident beam. The intensity and the polarization angle divergence of the combined beam are analyzed. The results show that the intensity profile of the diffracted beam is not changed remarkably compared to that of the input beam. The radially polarized beam can be obtained with a converting efficiency of 99.93% and the degree of radial polarization approaches a unit at a given polarization angle divergence value of 1 deg when the central alignment divergence is smaller than 0.025 mm.
It is an effective approach to obtain high-power laser output by spectral beam combining (SBC) technologies. The power
of the output beam increases with the increasing of the number of wavelength channels. However, that makes the
traditional SBC system very huge for achieving high power laser output. In this paper, a simple SBC system based on the
superimposed Reflective Volume Bragg Grating (RVBG) is proposed to reduce the scale of the SBC system. Two
structure models of the superimposed RVBG - the superimposed RVBG with the same period and the superimposed
RVBG with different period are analyzed and compared by using the rigorous coupled wave analysis, and their
applications for SBC system are discussed. Numerical results show that the superimposed RVBG are easy to be
fabricated and have the potential to combine multiple lasers with one volume. The superimposed RVBG with different
period can achieve high diffraction efficiency simultaneously for each grating with small slant angle divergence, and is
convenience to combine two beams with small spectral separation.
The regular spatial filters comprised of lens and pinhole are essential component in high power laser systems, such as
lasers for inertial confinement fusion, nonlinear optical technology and directed-energy weapon. On the other hand the
pinhole is treated as a bottleneck of high power laser due to harmful plasma created by the focusing beam. In this paper
we present a spatial filter based on angular selectivity of Bragg diffraction grating to avoid the harmful focusing effect in
the traditional pinhole filter. A spatial filter consisted of volume phase gratings in two-pass amplifier cavity were
reported. Two-dimensional filter was proposed by using single Pi-phase-shifted Bragg grating, numerical simulation
results shown that its angular spectrum bandwidth can be less than 160urad. The angular selectivity of photo-thermorefractive
glass and RUGATE film filters, construction stability, thermal stability and the effects of misalignments of
gratings on the diffraction efficiencies under high-pulse-energy laser operating condition are discussed.
An innovative configuration - two pieces of reflection volume phase gratings superposed is put forward, in order to
highly diffract the ultra-short laser pulse. Based on Kogelnik's coupled wave theory, and discrete Fourier transform, the
diffraction efficiency of the configuration for ultra-short laser pulse is formulated. And the diffraction efficiency for laser
pulse with a Gaussian shape in temporal domain is simulated. The results show that when the two gratings' vectors are
parallel to each other, and their parameters are selected appropriately, the diffraction spectrum of the configuration is
approximately composed of those of the two gratings. The diffraction efficiency of 70fs Gaussian laser pulse can be
improved to 0.96, which is 0.20 larger than that by only one piece of the grating. It is very useful for the application of
ultra-short laser pulse, such as beam deflector with high diffraction efficiency, spectral beam combination, and so on.